ABSTRACT
A focused ion beam (FIB) microscope has been used to simultaneously depth profile and image the gamma-gamma' microstructure of a nickel base superalloy using normal incidence milling in order to characterize the precipitate microstructure in three dimensions (3D). The normal incidence milling rates of the gamma and gamma' phases in this alloy are closely matched when the orientation of the depth-profiled surface is near 001, which allows for uniform material removal to depths up to a couple of microns. Depth-profiling experiments consisted of automated ion milling and collection of ion-generated secondary-electron images at specified intervals, and was demonstrated for a voxel resolution of roughly 15 x 15 x 16 nm(3). Image-processing software was used for automated processing of the 2D image sequence to render the gamma precipitate structure in 3D.
ABSTRACT
Through a combination of aberration-corrected high-resolution scanning transmission electron microscopy and three-dimensional atom probe tomography, the true atomic-scale structure and change in chemical composition across the complex order-disorder interface in a metallic alloy has been determined. The study reveals the presence of two interfacial widths, one corresponding to an order-disorder transition, and the other to the compositional transition across the interface, raising fundamental questions regarding the definition of the interfacial width in such systems.
